I see that these were ordered in April of last year. Has it been in service since then or did you just install it and find the issue?
The first thing I would do is remove the mounting plate completely and test the switch again. If nothing has been spilled on it and it wasn't exposed to any other nasty elements, it probably just needs to have the mounting plate loosened up a bit
Regardless, I put one in the mail for you today just in case.
RandyT